Thanks for the replies...so I came across a similar thing just now...it says that active sites of transcription show increased sensitivity to digestion with DNase (B-globin experiemnt)---so this must mean (putting it simply) that these sites are easily digestable??

Well, the concepts both use the word "sensitive," but they're not really the same idea. In the case of the receptor, increased sensitivity means tighter binding of an effector molecule (epinephrine). In the case of active gene transcription it's a statement about chromatin structure and accessibility to nucleases. Actively transcibed genes tend to be located in regions relatively free of nucleosomes and are therefore more exposed and in more open conformations. This makes the genes and their promoters more accessible to the RNA polymerase complex, but it also makes them accessible to attack by restriction endonucleases. Inactive genes, by contrast, tend to be tightly bound up on nucleosomes and are relatively inaccessible to either RNA polymerase or REs. Same word, sensitive, but different concepts.